protected void readGraphicControlExt()
    {
        read(); // block size
        int packed = read(); // packed fields
        dispose = (packed & 0x1c) >> 2; // disposal method
        if (dispose == 0)
        {
            dispose = 1; // elect to keep old image if discretionary
        }
        transparency = (packed & 1) != 0;
        delay = readShort() * 10; // delay in milliseconds
        transIndex = read(); // transparent color index
        read(); // block terminator
    }